1. Field of the Invention
The invention relates to the field of environmental control technology. In particular the invention relates to a method and system for the generation of high voltage, pulsed, periodic corona discharge.
2. Description of the Related Technology
Pulsed corona discharge based systems are among the most promising approaches in the field of environmental control technology. Such systems are used for the cleaning of water, air, furnaces, fuel and vent gases. The systems are also used as electro-precipitators with pulsed power supplies, as well as for ozone generation. Further development of these systems is limited by the lack of cost-effective and reliable power supplies that can generate short high voltage pulses and that have the necessary characteristics for industrial applications. Methods for matching these power supplies with a non-linear load of pulsed corona discharge are also lacking. This matching is desirable in order to achieve reasonable energy input efficiency into the pulsed corona discharge.
Today most of the methods for pulsed corona discharge generation are based on the use of thyratrons, which are gas-filled hot-cathode electron tubes in which the grid controls only the start of a continuous current thus giving the tubes a trigger effect, or triggered spark gaps (with a third electrode or rotating electrodes). These methods have the following drawbacks: Industrial thyratrons, as well as triggered spark gaps, are relatively expensive and have a short life time as generators of short pulses. Moreover, use of thyratrons or triggered spark gaps demands additional power for thyratron cathode heating, or for the formation of control pulses (triggering) or the rotation of electrodes. This reduces the overall energy efficiency of the pulse generator.
The use of untriggered spark gaps that have the best time characteristics when generating single pulses in conventional methods with ballast (serial) resistors results in very large energy losses during charging of the discharge capacitor (Ohmic heating loss can be more than 50%). Furthermore, the typical untriggered spark gap cannot provide the high frequencies of pulse generation (1000 Hz and higher) that are necessary for commercial applications of the pulsed corona discharges such as gas cleaning, or ozone generation.
Russian patent no. 2144257 discloses a device that was developed for generation of short pulses of high voltage for ignition of pulsed-periodic electric discharges like pulsed corona discharges or pulsed barrier discharges. The device can generate high voltage pulses with extremely short rise times (up to 5-10 ns) with high pulse repetition frequencies (about 2000 Hz) and with a maximal energetic efficiency of the device (COP on the level of 90%). The device comprises a high voltage power supply, a discharge capacitor, and a high voltage commutation switch that connects a discharge capacitor and a load. The high voltage power supply comprises a main rectifier, a semiconductor converter, and one or more pulsed high voltage transformers that provide charging of the discharge capacitor by small portions that form in each operation of the converter, so that the frequency of charging pulses of the discharge capacitor is at least three times larger than the frequency of the high voltage communication switch operation. The high voltage communication switch is made as an untriggered spark gap in which one or both electrodes are made in the form of one or several pins, threads, needles, blades or other components with sharp edges, so that corona discharge appears on these edges when the voltage between the gap electrodes is still below the breakdown voltage.
The method used in this above device has one important drawback: The residual high voltage exists on the electrodes of the pulsed corona chamber between corona pulses. This voltage corresponds to an extinguishing voltage of a corona discharge. Because of this drawback this device cannot be used for the generation of a corona discharge in the presence of droplets of water (e.g. spray, fog) or other conductive liquids in the discharge chamber. This option is extremely important for most commercial applications of the pulsed corona discharge for gas cleaning to enable hetero-phase plasma chemical reactions.
Therefore, there exists a need for providing a method and system for the generation of high voltage, pulsed, periodic corona discharges capable of being used in the presence of conductive liquid droplets.